class A {
    final double PI=3.1415926;// PI是常量
    public double getArea(final double r) {
      //r=r+1;//非法，不允许对final变量进行更新操作
      return PI*r*r;
    }
    public final void speak() {
      System.out.println("您好，How is everything here?");
    }
}
public class Example5_9 {
    public static void main(String args[]) {
      A a = new A();
      System.out.println("面积："+a.getArea(100));
      a.speak();
    }
}
